Field
Communication systems, such as the long term evolution (LTE) advanced (LTE-A) of the third generation partnership project (3GPP) may benefit from various enhancements. These enhancements can include LTE time division duplex (TDD) enhancements for traffic adaptation and uplink (UL)-downlink (DL) interference management.
Description of the Related Art
Currently, LTE TDD allows for asymmetric UL-DL allocations by providing seven different semi-statically configured TDD UL-DL configurations shown in FIG. 1. These allocations can provide between 40% and 90% DL subframes. The current mechanism for adapting UL-DL allocation is based on the system information change procedure with a 640 ms period. The concrete TDD UL/DL configuration is semi-statically informed by system information block, type 1 (SIB-1) signaling.
As shown in FIG. 1, the various UL-DL allocations can have either 5 ms or 10 ms switching point periodicity. Moreover, the allocations can include allocations for downlink, D, uplink U, and special S. The special subframes can be, for example, a guard period.
If dynamic TDD UL/DL reconfiguration is directly adopted in LTE systems including both homogeneous networks and heterogeneous networks, it may cause UL-DL interference in the conflicting subframes, due to independent and different TDD UL/DL configurations in neighboring cells, such as eNode B (eNB)-to-eNB interference and user equipment (UE)-to-UE interference. This kind of UL-DL interference can impact UL signal to interference plus noise ratio (SINR) when the eNBs are located in line of sight (LOS) or located close to each other or on DL SINK when the UEs are located at the edge of a cell.
Considering the impact of UL-DL interference, dynamic TDD UL/DL reconfiguration is mainly adopted in small cells, for example, pico cells, Femto cells, and LTE-Hi cells. As shown in FIG. 2, two small cells, cell 1 and cell 2, in the coverage of a macro cell can use a dynamic TDD UL/DL reconfiguration feature according to each cell's own uplink-downlink traffic variation while the macro cell uses a fixed TDD UL/DL configuration to avoid UL-DL interference in wide area network.
In this case, UE1 in DL served by a base station (BS) of cell 1 may receive interference from UE2 in the neighboring cell due to the uplink transmission of UE2. Likewise, UE2 in UL served by a BS of cell 2 may receive interference from BS of cell 1, due to the downlink transmission of Cell 1. In particular, when UE1 is located near UE2, interference may be greater between the two UEs. Similarly, when the two cells are located in LOS or close to each other, BS-to-BS interference may be greater between two BSs.
Currently, in real deployment, all the neighboring cells use the same TDD UL/DL configuration and thereby avoid the UL-DL interference explained above. Dynamically changing TDD UL/DL configuration brings new inter-cell interference scenarios such as eNB-to-eNB and UE-to-UE. So there is no specific conventional interference mitigation scheme with respect to this UL-DL interference.